A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus are conventionally used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, ultra high density hard disks, lens arrays, photonic band gap devices and other devices involving fine structures.
It is desirable to reduce the size of features in a lithographic pattern because this allows for a greater density of features on a given substrate area. In photolithography, the increased resolution may be achieved by using radiation of shorter wavelength. However, there are problems associated with such reductions. Current systems are starting to adopt optical sources with wavelengths in and below the 193 nm regime but even at this level, diffraction limitations become a barrier. At lower wavelengths, the transparency of materials is very poor. Optical lithography machines capable of enhanced resolutions require complex optics and rare materials and are consequently very expensive.
An alternative for printing sub-100 nm features, known as imprint lithography, comprises transferring a pattern to a substrate by imprinting a pattern into an imprintable medium using a physical mould or imprint template. The imprintable medium may be the substrate or a material coated on to a surface of the substrate. The imprintable medium may be functional or may be used as a “mask” to transfer a pattern to an underlying surface. The imprintable medium may, for instance, be provided as a resist deposited on a substrate such as a semiconductor material into which the pattern defined by the imprint template is to be transferred. Imprint lithography is thus essentially a molding process on a micrometer or nanometer scale in which the topography of a imprint template defines the pattern created on a substrate. Patterns may be layered as with optical lithography processes so that, in principle, imprint lithography could be used for such applications as IC manufacture.
The resolution of imprint lithography is typically limited only by the resolution of the imprint template fabrication process. For instance, imprint lithography may be used to produce features in the sub-50 nm range with significantly improved resolution and line edge roughness compared to that achievable with a conventional optical lithography process. In addition, an advantage of imprint processes includes that they generally do not require expensive optics, advanced illumination sources or specialized resist materials that are often required in optical lithography processes.
Current imprint lithography processes may have one or more drawbacks as will be mentioned below, particularly with regard to achieving overlay accuracy and/or high throughput. However the significant improvement in resolution and/or line edge roughness attainable from imprint lithography is a strong driver for addressing one or more of those or other drawbacks.